Water Pump

ABSTRACT

A water pump includes a pump shaft surrounded by a pump housing having a tubular section. A pulley having a cylindrical section and a flange wall is mounted on an end section of the pump shaft. An impeller is mounted on the other end section of the pump shaft. A mechanical seal is coaxially disposed between the tubular section and the pump shaft. A bearing is coaxially disposed between the tubular section of the pump housing and the cylindrical section of the pulley. In this water pump, the pump shaft includes a coaxial small diameter shaft section located at its first part which is located axially between the mechanical seal and the flange wall. The small diameter shaft section has a diameter smaller than a diameter of a second part of the pump shaft on which the mechanical seal is disposed so as to form an annular step portion.

BACKGROUND OF THE INVENTION

This invention relates to a water pump, for example, for supplying the inside of an engine with coolant.

A water pump as disclosed in Japanese Patent Provisional Publication No. 2004-84610 is known as one for supplying the inside of an engine with coolant. In summary, the water pump includes a pump housing inside which a pump shaft formed integral with a pulley under press-forming is disposed and rotatably supported through a ball bearing. Additionally, an impeller is fixed on a tip end section of the pump shaft. The ball bearing has an outer race fixed to the inner peripheral portion of the pulley and an inner race fixed on the outer peripheral surface of the tubular section of the pump housing. Additionally, a mechanical seal is disposed between the pump shaft and the pump housing to prevent coolant from leaking in a direction of from a pump chamber for rotatably accommodating the impeller to the ball bearing.

SUMMARY OF THE INVENTION

However, in the water pump as disclosed in the above publication, it is difficult to completely prevent leaking of coolant from the pump chamber by the mechanical seal from the viewpoint of a structure. Accordingly, there is a fear that coolant leaking through the mechanical seal transfers through the outer peripheral surface of the pump shaft so as to penetrate into the ball bearing. As a result, the durability of the ball bearing unavoidably degraded owing to rust formation and the like.

In view of the above actual conditions of the conventional water pump, an improved water pump according to the present invention has been devised. An object of the present invention is to provide the improved water pump configured to prevent coolant leaking through a mechanical seal from transferring through the pump shaft toward the bearing so that no coolant reaches the bearing.

An aspect of the present invention resides in a water pump comprising a pulley including a cylindrical section located radially inward of an outer periphery of the pulley, the pulley being rotatable upon transmission of power from a driving force. A pump shaft is disposed radially inward of the cylindrical section of the pulley and fixed to the cylindrical section, the pump shaft having a first end section on which the pulley is mounted. A flange wall extends from an axial end portion of the cylindrical section of the pulley in a direction of the pump shaft. An impeller is disposed at a second end section of the pump shaft. A pump housing includes a tubular section disposed to surround the pump shaft. A mechanical seal is disposed between a radially inward side of the tubular section of the pump housing and an outer peripheral surface of the pump shaft. Additionally, a bearing is disposed between an inner peripheral surface of the cylindrical section of the pulley and the tubular section of the pump housing to rotatably support the pulley on the tubular section of the pump housing. In the above water pump, the pump shaft includes a coaxial small diameter shaft section located at its first part which is located axially between the mechanical seal and the flange wall. The small diameter shaft section has a diameter smaller than a diameter of a second part of the pump shaft on which the mechanical seal is disposed. The small diameter shaft section has an outer peripheral surface located radially inward of an outer peripheral surface of a third part of the pump shaft axially extending from the second part so as to form an annular step portion.

Another aspect of the present invention resides in a water pump comprising a pulley including a cylindrical section located radially inward of an outer periphery of the pulley, the pulley being rotatable upon transmission of power from a driving force. A pump shaft is disposed radially inward of the cylindrical section of the pulley and fixed to the cylindrical section, the pump shaft having a first end section on which the pulley is mounted. A flange wall extends from an axial end portion of the cylindrical section of the pulley in a direction of the pump shaft. An impeller is disposed at a second end section of the pump shaft. A pump housing includes a tubular section disposed to surround the pump shaft. A mechanical seal is disposed between a radially inward side of the tubular section of the pump housing and an outer peripheral surface of the pump shaft. A bearing is disposed between an inner peripheral surface of the cylindrical section of the pulley and the tubular section of the pump housing to rotatably support the pulley on the tubular section of the pump housing. In the above water pump, the pump shaft includes a step portion located axially between the mechanical seal and the flange wall to restrict movement of adhering water transferred through the outer peripheral surface of the pump shaft from side of the mechanical seal in a direction toward the flange wall.

A further aspect of the present invention resides in a water pump comprising a pump shaft having a first end section on which a pulley is disposed and a second end section on which an impeller is disposed. A pump housing is disposed surrounding an outer peripheral side of the pump shaft. A bearing is disposed to the pump housing to rotatably supporting the pump shaft. A mechanical seal is fixed to the pump housing and to the pump shaft and having a seal section which makes sliding at a position nearer to the impeller than to the bearing in an axial direction of the pump shaft. In the above water pump, a coaxial and annular groove is formed at the outer peripheral surface of the pump shaft and located at an axial position between the mechanical seal and the bearing to prevent adhering water from transferring in a direction toward the bearing.

The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference numerals designate like parts and elements throughout all figures, in which:

FIG. 1 is a vertical sectional view of a first embodiment of a water pump according to the present invention;

FIG. 2 is an exploded perspective view of the water pump of FIG. 1;

FIG. 3 is a fragmentary front elevation showing an essential part of a second embodiment of the water pump according to the present invention;

FIG. 4 is a fragmentary front elevation partly in section showing an essential part of a third embodiment of the water pump according to the present invention;

FIG. 5 is a fragmentary front elevation partly in section showing an essential part of a fourth embodiment of the water pump according to the present invention;

FIG. 6 is a fragmentary front elevation showing an essential part of a fifth embodiment of the water pump according to the present invention;

FIG. 7 is a fragmentary front elevation showing an essential part of a sixth embodiment of the water pump according to the present invention;

FIG. 8 is a fragmentary front elevation showing an essential part of a seventh embodiment of the water pump according to the present invention; and

FIG. 9 is a fragmentary front elevation showing an essential part of an eighth embodiment of the water pump according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 and 2 of drawings, a first embodiment of a water pump according to the present invention is illustrated by the reference numeral 1. Water pump 1 is applied for a cooling system in which coolant containing anti-freezing liquid (ethylene glycol) is circulated between a radiator (not shown) and an engine (not shown) of an automotive vehicle. Water pump 1 is directly installed to a side section of a cylinder block (not shown) of the engine by means of bolt-securing or the like. Water pump 1 includes a pump housing 2 having a part of a pump chamber 3. Another part of pump chamber 3 is formed in a front end section of the cylinder block. A pulley 4 is rotatably supported on an outer peripheral side of pump housing 2 through a single ball bearing 5. A pump shaft 6 is axially disposed inside pump housing 2 and has a front or first end section 6 a fixed to the pulley 4. An impeller 7 is fixed on a rear or second end section 6 b of pump shaft 6 and rotatably accommodated in pump chamber 3. A mechanical seal 8 is interposed between pump housing 2 and pump shaft 6 to establish sealing between pump chamber 3 and ball bearing 5.

Pump housing 2 is made of, for example, an aluminum alloy and formed into a one-piece structure. Pump housing 2 includes a pump housing main body 9 and a tubular or cylindrical section 10 integral with main body 9. Pump housing main body 9 is located to define the part of pump chamber 3 and is formed into a deformed annular shape. Tubular section 10 is formed integral with housing main body 9 at a front end side and formed axially step-like and diametrically changing. Housing main body 9 is formed at its rear end with an annular and flat installation face 9 a which is in contact with a flat surface portion located at a side section of the cylinder block. Housing main body 9 includes an outer peripheral section (no numeral) having a plurality of boss portions 9 c each of which is formed with a bolt-hole 9 b in which an installation bolt (not shown) is to be inserted. Additionally, this housing main body 9 is formed thereinside with a discharge port 9 d through which coolant flowing into pump chamber 3 from a suction port (not shown) communicated with the radiator is discharged into the water jacket of the cylinder block under the rotation of impeller 7.

As shown in FIGS. 1 and 2, tubular section 10 includes a large diameter portion 10 a located at the side of pump chamber 3. An intermediate diameter portion 10 b is coaxially integral with large diameter portion 10 a and axially extends in the direction of ball bearing 5 from large diameter portion 10 a. A small diameter portion 10 c is coaxially integral with intermediate diameter portion 10 b and axially extends in the direction of front end portion 6 a of pump shaft 6 from intermediate diameter portion 10 b. Accordingly, a diametrically stepwise space 10 d is formed inside the tubular section 10.

Intermediate diameter portion 10 b is formed with a drain hole 11 which is vertically extends to pass through the wall of intermediate diameter portion and located at its lower side so that water droplets of coolant leaking through mechanical seal 8 is flown downward from the drain hole. A drain chamber 12 is formed below the drain hole 11 and extends to large diameter portion 10 a in order to collect and store water droplets dropped from drain hole 11. This drain chamber 12 has a lower end opening (no numeral) which is fluidly sealed with a cap 13.

Additionally, intermediate diameter portion 10 b is formed with a vent opening located at an upper side in the direction of gravity in order to discharge water vapor of coolant leaking from mechanical seal 8 or stored within drain chamber 12, to the outside of water pump 1 or into the atmosphere. Further, intermediate diameter portion 10 b is formed at its inner peripheral side with an annular space chamber 15 which is defined between the inner wall of intermediate diameter portion 10 b and the outer peripheral surface of pump shaft 6. This annular space chamber 15 is vertically communicated with drain hole 11 and vent opening 14. Furthermore, intermediate diameter portion 10 b has a cylindrical protruding portion 10 f which is integrally formed protruding from the outer peripheral surface of intermediate diameter portion 10 b. Cylindrical protruding portion 10 f is formed thereinside with a vent communication opening 18 through which vent opening 14 is in communication with the atmosphere.

As shown in FIGS. 1 and 2, pulley 4 is formed into a generally disc-shaped one piece structure by press-forming a metal plate material. Pulley 4 includes a centrally located cylindrical or cup-shaped fixing section 4 a into which front end section 6 a of pump shaft 6 is press-fitted to be fixed there. An annular disc-shaped first flange wall 4 b is integral with fixing section 4 a and radially extends from the peripheral portion of an axially one end of fixing section 4 a. A large diameter cylindrical section 4 c is integral with first flange wall 4 b and axially extends from the outer peripheral portion of flange wall 4 b. An annular disc-shaped large diameter second flange wall 4 d is integral with cylindrical section 4 c and generally radially extends from the peripheral portion of an axially one end of the cylindrical section 4 c. A generally cylindrical belt installation section 4 e is integral with second flange wall 4 d and axially extends from the outer peripheral portion of second flange wall 4 d.

Fixing section 4 a is formed with an air vent opening 4 f which is located at the central part of fixing section 4 a to pierce the wall of the central part in order to accomplish a smooth press-fitting operation for pump shaft 6. A cover member 17 which will be discussed after is press-fitted on fitting section 4 a at the outer peripheral surface.

As illustrated in FIG. 2, flange wall 4 b is formed with a plurality of through-holes 16 which are arranged at circumferentially generally equal intervals and along a circumference which is located at a radially central part of flange wall 4 b. These through-holes 16 serve as operational holes through which jigs (not shown) for press-fitting are inserted when an inner race 5 a of ball bearing 5 is press-fitted on the outer peripheral surface of small diameter portion 10 c of tubular section 10. Besides, these through-holes 16 serve to discharge water vapor vaporized from the inside of drain chamber 12 and reaching the inside of small diameter portion 10 c, to the outside. Accordingly, the position or the diameter of each through-hole 16 is suitably set to accomplish the above-discussed serves.

Cylindrical section 4 c of pulley 4 is so configured that outer race 5 b of ball bearing 5 is press-fitted and fixed inside the cylindrical section 4 c at the inner peripheral surface. Accordingly, the axial length of cylindrical section 4 c is slightly larger than that of outer race 5 b of ball bearing 5, and the inner diameter of cylindrical section 4 c is slightly smaller that the outer diameter of outer race 4 c to effectively accomplish the press-fitting of ball bearing 5.

Second flange wall 4 d of pulley 4 formed bent to protrude in the direction of impeller 7 thereby obtaining a stiffness thereof.

Belt installation section 4 e of pulley 4 includes an outer peripheral portion having annular projections each of which projects radially outward and has a generally triangular cross-section. A transmission belt (not shown) passed on a drive pulley (not shown) fixed on a tip end section of a crankshaft (not shown) of the engine is further passed on the outer peripheral portion of belt installation section 4 e so that a rotational force of the crankshaft is transmitted to pulley 4.

Cover member 17 is formed of a thin metal plate and generally cup-shaped. Cover member 17 is disposed in such a manner as to cover the front surfaces of first flange wall 4 b, cylindrical section 4 c and second flange wall 4 d. Additionally, cover member 17 has a centrally located cylindrical section 17 a which is press-fitted and fixed on the outer peripheral surface of fixing section 4 a of the pulley 4. An annular disc section 17 b is integral with cylindrical section 17 a and radially outwardly extends from the peripheral portion of an axial end of the cylindrical section 17 a. The inner surface of disc section 17 b covers the whole opposite surface of first flange wall 4 b and disposed opposite to first flange wall 4 b forming an annular space S between the disc section 17 b and first flange wall 4 b. Further, a large diameter section 17 c is integral with disc section 17 b and radially outwardly extends from the outer peripheral portion of disc section 17 b. Large diameter section 17 c is formed tapered in a direction of from rear end section 6 b to the front end section 6 a of pump shaft 6. An annular outer peripheral section 17 d is integral with large diameter section 17 c and radially outwardly extends from the outer peripheral portion of large diameter section 17 c. Outer peripheral section 17 d is perpendicular to the axis of pump shaft 6 and disposed opposite to the inner peripheral surface of belt installation section 4 e forming a clearance S3 while opposite to the front or inner surface of the second flange wall 4 d forming a slight annular clearance S1. Accordingly, this cover member 17 closes the front end parts of through-holes 16 of first flange wall 4 b thereby preventing penetration of dusts and the like from the outside while discharging water vapor evaporated from drain chamber 12 and the like and passing through through-holes 16, to the outside through clearances S, S1, S3.

Ball bearing 5 is a general one and includes inner race 5 a press-fitted on small diameter portion 10 c, outer race 5 b press-fitted in cylindrical section 4 c, and a plurality of balls 5 c rotatably disposed between inner and outer races 5 a, 5 b through a retainer. An axial maximum press-fit position of inner race 5 a is restricted by an annular projection 10 e formed at the front end portion of intermediate diameter portion 10 b of tubular section 10. An axial position of outer race 5 b can be set according to the positioning of inner race 5 a when the inner race is press-fitted in cylindrical portion 4 c. Additionally, an annular clearance S2 is formed between the front end portion of ball bearing 5 and first flange wall 4 b so as to introduce water vapor and the like toward through-holes 16.

A front bearing seal 19 a and a rear bearing seal 19 b are respectively disposed at the front and rear end portions of inner and outer races 5 a, 5 b in order to prevent penetration of ducts and the like into the ball bearing 5. Each bearing seal 19 a, 19 b is formed of an annular rubber material and has an outer peripheral portion fixed to an axial end portion of outer race 5 b and an inner peripheral portion slidably secured to an axial end portion of inner race 5 a thereby accomplishing sealing for the inside of ball bearing 5.

Additionally, also as illustrated in FIG. 2, a shield plate 20 formed of a thin and annular plate is fixed upon being interposed between inner race 5 a and annular projection 10 e of intermediate diameter portion 10 b. This shield plate 20 is disposed in such a manner as to cover the rear end side or face of ball bearing 5 to prevent penetration of dusts and the like into ball bearing 5 from the outside.

As shown in FIGS. 1 and 2, pump shaft 6 is formed of a metal material and has a generally equal outer diameter throughout whole the length. Pump shaft 6 is formed at its outer peripheral surface 6 c with a coaxial annular groove under cutting-out thereby defining a small diameter shaft section 21, located at a generally axially central part of pump shaft 6. This small diameter shaft section 21 is formed at a position between mechanical seal 18 and first flange wall 4 b, i.e., at a position abutting on annular space chamber 15 so that the small diameter shaft section 21 is located inside annular space chamber 15. Small diameter shaft section 21 is interposed between a first annular face 22 at the side of mechanical seal 8 and a second annular face 23 at the opposite side. The outer peripheral surface of pump shaft 6 is contiguous with the outer peripheral surface of small diameter shaft section 21 through each of first and second annular faces 22, 23, forming an annular step portion.

Each of first and second annular faces 22, 23 is formed perpendicular to the axis of pump shaft 6 and respectively have outer peripheries 22 a, 23 a which abut on or face to drain hole 11 and vent opening 14 through annular space chamber 15. Additionally, small diameter shaft section 21 has an axial length W of about 2 mm, corresponding to a width (W) between first and second annular faces 22, 23. A radial width D of each of first and second annular faces 22, 23 is set to be about 1 mm. The radial width D corresponds to a depth of the annular groove defined between first and second annular faces 22, 23, or a radial distance between the outer peripheral surface of small diameter shaft section 21 and the outer peripheral surface of pump shaft 6. It is to be noted that the above-mentioned length W and distance D may be respectively set to be not less than 2 mm and not less than 1 mm.

Impeller 7 is formed as a one-piece structure by press-forming and includes a cylindrical press-fitted fixing section 7 a which is press-fitted and fixed on rear end section 6 b of pump shaft 6. A plurality of blades 7 b are integral with fixing section 7 a and radially extend from an axially end portion of fixing section 7 a. Fixing section 7 a is formed at its central part with an air vent opening 7 c for the purpose of smoothing a press-fit operation of pump shaft 6.

Mechanical seal 8 is a general one and includes a cartridge section 8 a fixed to the inner peripheral surface of intermediate diameter portion 10 b of tubular section 10. A sleeve section 8 b is supported on outer peripheral surface 6 c of pump shaft 6. A seal section 8 c is disposed between the inner peripheral surface of cartridge section 8 a and the outer peripheral surface of sleeve section 8 b and configured to make a fluid tight seal under sliding.

With the above arranged embodiment, when the crankshaft of the engine (driving source) is rotated to drivingly rotate pulley 4, impeller 7 is rotated through pump shaft 6 to make a pumping action so that coolant is fed under pressure from discharge port 9 d to the water jacket of the engine thereby accomplishing cooling of the engine.

At this time, a major part of high pressure coolant in pump chamber 3 is prevented from flowing to the side of the front end section of pump shaft 6 under the action of mechanical seal 8; however, a part of high pressure coolant leaks out through sliding seal section 8 c of mechanical seal 8 and flows through outer peripheral surface 6 c of pump shaft 6 to the side of the front end section 6 a of pump shaft 6. When this flowing coolant reaches first annular face 22 of pump shaft 6, it splashes outwardly from outer periphery 22 a of the first annular face 22 to reach annular space chamber 15 under a centrifugal force due to rotation of pump shaft 6, followed by dropping through drain hole 11 into drain chamber 12 to be collected and stored there. Specifically, since first annular face 22 is formed perpendicular to the axis of pump shaft 6, coolant transferring through outer peripheral surface 6 c of pump shaft 6 is rapidly cut at outer periphery 22 a of first annular face 22 and splashes outwardly, and then drops through drain hole 11 into drain chamber 12 to be stored there. Accordingly, almost whole coolant leaking through mechanical seal 8 can be prevented from reaching the side of second annular face 23 through the outer peripheral surface of small diameter shaft section 21 under effective coolant cutting and splashing effects by first annular face 22.

Additionally, even if a small amount of coolant flows through the outer peripheral surface of small diameter shaft section 21 to the side of front end section 6 a of pump shaft 6, it flows to second annular face 23 and cut by outer periphery 23 a of second annular face 23 so as to splash outwardly thereby being drained into drain chamber 12. This coolant stored in drain chamber 12 vaporizes to form water vapor. A major part of water vapor of coolant leaking through mechanical seal 8 is discharged out of water pump 1 though annular space chamber 15 and the vent opening 14. Even in case that this water vapor flows from annular space chamber 15 into annular clearance S2 through a cylindrical passage 24 formed between the outer peripheral surface of pump shaft 6 and the inner peripheral surface of small diameter portion 10 c of tubular section 10, it flows into the clearance S through through-holes 16 and then moves through a clearance between cover member 17 and pulley 4 to be discharged out from annular clearances S1, S3.

As discussed above, almost whole coolant which leaks through mechanical seal 8 to be flown into small diameter shaft section 21 through outer peripheral surface 6 c of pump shaft 6 can be effectively cut and splash so as to drop into drain chamber 12 through drain hole 11, thereby sufficiently preventing coolant leaking through mechanical seal 8 from flowing into ball bearing 5. Furthermore, even if a small amount of coolant flows through the outer peripheral surface of small diameter shaft section 21 of pump shaft 6 to the side of front end section 6 a of pump shaft 6, it can be effectively cut by and splash from outer periphery of second annular face 23 so as to be drop into drain chamber 12 through drain hole 11 thereby sufficiently preventing it from penetration into ball bearing 5. Moreover, water vapor discussed above is also smoothly discharged out of water pump 1 through vent opening 14, annular clearance S2, through-holes 16 and clearances S, S1, S3 thereby preventing it from penetration into ball bearing 5. Additionally, the inside of ball bearing 5 is sealed with bearing seals 19 a, 19 b, thereby making it possible to further prevent coolant and water vapor from penetration into ball bearing 5.

Further, cover 17 can prevent penetration of dusts and the like into ball bearing 5 through through-holes 16 from the outside. Besides, under the action of shield plate 20, penetration of dusts and the like into ball bearing 5 through the outside around the intermediate portion 10 b of cylindrical section 19 can be prevented.

As a result, formation of rust inside ball bearing 5 can be effectively prevented while avoiding penetration of dusts and the like into the ball bearing 5, thus improving the durability of ball bearing 5.

Furthermore, the outer peripheral surface of small diameter shaft section 21 of the pump shaft is formed simply cylindrical, and therefore the small diameter shaft section can be readily formed by machining such as cutting or grinding.

Hereinafter, discussion will be made on a variety of further embodiments including respectively modified examples of configurations each of which is around small diameter shaft section 21 of pump shaft 6, with reference to FIGS. 3 to 9 in which the same reference numerals as those in the first embodiment designate like parts and elements.

FIG. 3 illustrates an essential part of a second embodiment of the water pump according to the present invention, in which small diameter shaft section 21 of pump shaft 6 is extended to the tip end of front end section 6 a so that the diameter of the front end section is equal to that of the small diameter shaft section. Accordingly, only first annular face 22 exists so that no second annular face (23) exists; however, coolant or water flowing through outer peripheral surface 6 c of pump shaft 6 can be effectively cut and splash under the action of first annular face 22.

FIG. 4 illustrates an essential part of a third embodiment of the water pump according to the present invention, in which small diameter section 21 of pump shaft 6 is extended to the tip end of front end section 6 a similarly to in the second embodiment. First annular face 22 is frustoconical and tapered in a direction toward the mechanical seal so that an inner periphery (no numeral) of first annular face 22 is axially withdrawn in a direction toward mechanical seal 8 relative to outer periphery 22 a. Thus, an outer peripheral portion (including outer periphery 22 a) of the annular step portion is formed having an acute angle in section. Accordingly, with this embodiment, coolant or water flowing through outer peripheral surface 22 a in a direction of from the side of mechanical seal 8 to small diameter shaft section 21 is securely cut and splash under the action of the sharp edge-like outer peripheral portion. As a result, a water cutting and splashing effect can be further improved thereby sufficiently preventing water from transferring to small diameter shaft section 21.

FIG. 5 illustrates an essential part of a fourth embodiment of the water pump according to the present invention, in which first annular face 22 is frustoconical and tapered in a direction toward the mechanical seal so that an outer peripheral portion (including outer periphery 22 a) of the annular step portion is formed having an acute angle in section, similarly to in the third embodiment. Second annular face 23 is formed perpendicular to the axis of pump shaft 6.

Accordingly, the similar effect as in the third embodiment can be obtained by the first annular face 22. Additionally, even if a small amount of coolant or water is transferred through the outer peripheral surface of small diameter section 21, it can be cut and splash by second annular face 23.

FIG. 6 is an essential part of a fifth embodiment of the water pump according to the present invention, in which first annular face 22 is formed perpendicular to the axis of pump shaft 6 similarly to in the first and second embodiments whereas the second annular face 23 is formed frustoconical and tapered in a direction toward the mechanical seal 8 so that the inner periphery of second annular face 23 is axially withdrawn in a direction toward the mechanical seal relative to outer periphery 23 a.

With this embodiment, effective water cutting and splashing actions can be obtained by first annular face 23. Furthermore, since second annular face 23 is formed tapered in the direction toward the mechanical seal, water cutting and splashing actions are reduced; however, the rigidity of pump shaft 6 is increased thereby suppressing development of a concentrated stress in a direction of bending.

FIG. 7 illustrates an essential part of a sixth embodiment of the water pump according to the present invention, which is basically similar to the first embodiment with the exception that the outer peripheral surface 6 c of pump shaft 6 is formed gently tapered in a direction of from the side of front end section 6 a to the side of rear end section 6 b. Accordingly, an outer peripheral portion (including outer periphery 22 a) of the annular step portion is naturally formed having a large acute angle in section, whereas an outer peripheral portion (including an outer periphery 23 a) of the other annular step portion is naturally formed having a small obtuse angle in section.

Hence, a good water cutting and splashing effect can be obtained particularly by the outer peripheral portion (including outer periphery 22 a) of the annular step portion including first annular face 22.

FIG. 8 illustrates an essential part of a seventh embodiment of the water pump according to the present invention, in which first annular face 22 includes coaxial two annular faces (no numerals) which are different in diameter and axially separate from each other so that the two annular faces are connected through a cylindrical outer peripheral surface which is smaller in diameter than outer peripheral surface 6 c of pump shaft 6 thereby to form first two annular step portions, while first annular face 23 includes coaxial two annular faces (no numerals) which are different in diameter and axially separate from each other so that the two annular faces are connected through a cylindrical outer peripheral surface which is smaller in diameter than outer peripheral surface 6 c of pump shaft 6 thereby to form second two annular step portions, in which first and second annular faces 22, 23 are generally symmetrical to each other. Thus, the first two annular step portions respectively including outer peripheries 22 a, 22 b are formed around first annular face 22, while the second two annular step portions respectively including outer peripheries 23 a, 23 b are formed around second annular face 22.

Accordingly, an effective water cutting and splashing effect can be obtained by the two annular step portions (respectively including outer peripheries 22 a, 22 b), and additionally water cutting and splashing actions can be accomplished by the other two annular step portions (including outer peripheries 23 a, 23 b). Furthermore, each of the first and second annular step portions is formed step-like thereby suppressing developing of a concentrated stress of bending deformation.

FIG. 9 illustrates an essential part of a fifth embodiment of the water pump according to the present invention, which is basically similar to the first embodiment with the exception that small diameter shaft section 21 of pump shaft 6 is integrally provided with a coaxial annular projection section 25 which is located at its axially central part and has an outer diameter equal to that of pump shaft 6. Annular projection section 25 projects radially outward from the outer peripheral surface of small diameter shaft section 21 and has opposite annular faces 25 a, 25 b which are perpendicular to the axis of pump shaft 6. In this embodiment, first and second annular faces 22, 23 are perpendicular to the axis of pump shaft 6 similarly to annular faces 25 a, 25 b.

Accordingly, the almost whole water flown upon being transferred through outer peripheral surface 6 c of pump shaft 6 is first cut and splash by outer periphery 22 a of first annular face 22. Even if a part of such water flows in a direction of annular projection section 25 through the outer peripheral surface of small diameter shaft section 21, it is further cut and splashes by outer periphery 25 c of annular face 25 a of annular projection section 25 so as to drop in a direction of drain hole 11. Hence, under such double water cutting and splashing actions, water hardly flows in a direction of second annular face 23 over annular face 25 a. Even if a part of water flows in the direction of second annular face 23, water can be cut and splash by outer periphery 25 d of annular face 25 b of the annular projection section 25 and by outer periphery 23 a of second annular face 23 so as to be prevented from flowing in a direction toward ball bearing 5. Additionally, by virtue of annular projection section 25, small diameter shaft section 21 of pump shaft 6 is increased in its strength thereby making it possible to be sufficiently endurable to bending deformation and torsional deformation.

The present invention is not limited to the above embodiments, in which, for example, the axial length W of small diameter shaft section 21 and the radial width D of first or second annular face 22, 23 may be changed, and a tapering angle of the tapered or frustoconical first or second annular face 22, 23 may be changed. Additionally, while ball bearing 5 has been shown and described to be used as a bearing for pulley 4, it will be appreciated that it may be replaced with, for example, a plane bearing or a needle bearing. Further, although first annular face 22 has been shown and described as being formed perpendicular to the axis of pump shaft 6 in the first embodiment or the like, it will be understood that the first annular face may be formed slightly tapered in a direction toward mechanical seal 8 or in a direction toward ball bearing 5 forming a small angle (in section) to a plane perpendicular to the axis of pump shaft 6.

Next, discussion will be made technical ideas (a) to (q) grasped from the above embodiments, other than those recited in claims.

A basic idea of the present invention resides in a water pump comprising: a pulley including a cylindrical section located radially inward of an outer periphery of the pulley, the pulley being rotatable upon transmission of power from a driving force; a pump shaft disposed radially inward of the cylindrical section of the pulley and fixed to the cylindrical section, the pump shaft having a first end section on which the pulley is mounted; a first flange wall extending from a first axial end portion of the cylindrical section of the pulley in a direction of the pump shaft; an impeller disposed at a second end section of the pump shaft; a pump housing including a tubular section disposed to surround the pump shaft; a mechanical seal disposed between a radially inward side of the tubular section of the pump housing and an outer peripheral surface of the pump shaft; and a bearing disposed between an inner peripheral surface of the cylindrical section of the pulley and the tubular section of the pump housing to rotatably support the pulley on the tubular section of the pump housing; wherein the pump shaft includes a coaxial small diameter shaft section located at its first part which is located axially between the mechanical seal and the flange wall, the small diameter shaft section having a diameter smaller than a diameter of a second part of the pump shaft on which the mechanical seal is disposed, the small diameter shaft section having an outer peripheral surface located radially inward of an outer peripheral surface of a third part of the pump shaft axially extending from the second part so as to form a first annular step portion.

(a) In the water pump as recited in the basic idea, the outer peripheral surface of the small diameter shaft section of the pump shaft is cylindrical.

With this idea, since the outer peripheral surface of the small diameter shaft section is simply cylindrical, the small diameter shaft section can be readily formed by cutting or grinding.

(b) In the water pump as recited in the basic idea, the small diameter shaft section of the pump shaft is formed at a part of the pump shaft. The diameter of the small diameter shaft section is smaller than a diameter of a fourth part of the pump shaft extending to the first end section of the pump shaft. The outer peripheral surface of the small diameter shaft section is located radially inward of an outer peripheral surface of the fourth part of the pump shaft so as to form a second annular step portion.

With this idea, even if water is transferred through the outer peripheral surface of the small diameter shaft section so as to move to the side of the flange wall, water can be cut and splash by the periphery of an annular face forming the second step portion, thereby effectively restricting movement of water in a direction toward the flange wall, i.e., in a direction toward the bearing.

(c) In the water pump as recited at (b5), the outer peripheral surface of the fourth part of the pump shaft and the outer peripheral surface of the small diameter shaft section are connected to each other through at least one annular face which is perpendicular to an axis of the pump shaft or tapered in a direction away from the first flange wall.

With this idea, since the second annular step portion is formed tapered, the strength of the pump shaft is increased.

(d) In the water pump as recited in the basic idea, the tubular section of the pump housing includes a first portion defining thereinside a drain chamber for storing a liquid having a volume, and a second portion defining a drain hole for introducing liquid dropped from the annular step portion into the drain chamber. The drain chamber and the drain hole are located under the annular step portion in a direction of gravity. The drain chamber is open to the atmosphere.

With this idea, liquid stored in the drain chamber is evaporated to release to the atmosphere.

(e) In the water pump as recited at (d), the tubular section of the pump housing includes a third portion defining thereinside an annular space chamber located around the outer peripheral surface of the small diameter shaft section, and a fourth portion defining a vent opening for venting vapor. The drain hole is formed above the annular space chamber in the direction of gravity, while the vent opening is formed below the annular space chamber in the direction of gravity.

(f) In the water pump as recited in the basic idea, the pump shaft is formed continuously tapered in an axial direction of from the side of the flange wall to the side of the impeller. The outer peripheral surface of the third part of the pump shaft and the outer peripheral surface of the small diameter shaft section are connected through at least one annular face forming the first annular step portion, the annular face being perpendicular to the axis of the pump shaft.

With this idea, water transferred through the tapered outer peripheral surface of the pump shaft from the side of the mechanical seal can be effectively cut and splash by a peripheral portion having an acute angle, formed by the tapered outer peripheral surface and the annular face.

(g) In the water pump as recited in the basic idea, the pulley includes a second flange wall extending from the cylindrical section at a second axial end portion opposite to the first axial end portion, and a belt installation section which axially extends from the outer peripheral portion of the second flange wall.

(h) In the water pump as recited in the basic idea, the pulley and the first flange wall are formed integral with each other.

(i) In the water pump as recited at (h), the pump shaft and the first flange wall are formed separate from each other, in which the first end section of the pump shaft is fixed to the first flange wall.

(j) In the water pump as recited in the basic idea, the first flange wall is formed with a plurality of through-holes.

With this idea, by using these through-holes, the bearing can be fixed between the cylindrical section of the pulley and the tubular section of the pump housing from an axial direction with a jig, and water vapor passed through the mechanical seal can be discharged to the outside.

(k) In the water pump as recited in the basic idea, the first annular step portion is formed to have a plurality of annular step portions.

(l) In the water pump as recited at (k), the small diameter shaft section includes a plurality of coaxial small diameter shaft sections so as to form a plurality of annular step portions.

(m) In the water pump as recited in the basic idea, the bearing includes an inner race, an outer race, and a bearing seal which is fixed to one of the inner and outer races and slidable to the other race.

By virtue of this bearing seal, water and the like can be prevented from penetrating to the inside of the bearing.

(n) In the water pump as recited in the basic idea, the outer peripheral surface of the small diameter shaft section is located radially inward of the outer peripheral surface of the third part of the pump shaft by not less than 1 mm which corresponds to a height of the annular step portion.

(o) A water pump comprising: a pulley including a cylindrical section located radially inward of an outer periphery of the pulley, the pulley being rotatable upon transmission of power from a driving force; a pump shaft disposed radially inward of the cylindrical section of the pulley and fixed to the cylindrical section, the pump shaft having a first end section on which the pulley is mounted; a flange wall extending from an axial end portion of the cylindrical section of the pulley in a direction of the pump shaft; an impeller disposed at a second end section of the pump shaft; a pump housing including a tubular section disposed to surround the pump shaft; a mechanical seal disposed between a radially inward side of the tubular section of the pump housing and an outer peripheral surface of the pump shaft; and a bearing disposed between an inner peripheral surface of the cylindrical section of the pulley and the tubular section of the pump housing to rotatably support the pulley on the tubular section of the pump housing; wherein the pump shaft includes a step portion located axially between the mechanical seal and the flange wall to restrict movement of adhering water transferred through the outer peripheral surface of the pump shaft from the side of the mechanical seal in a direction toward the flange wall.

(p) A water pump comprising: a pump shaft having a first end section on which a pulley is disposed and a second end section on which an impeller is disposed; a pump housing disposed surrounding an outer peripheral side of the pump shaft; a bearing disposed to the pump housing to rotatably supporting the pump shaft; and a mechanical seal fixed to the pump housing and to the pump shaft and having a seal section which makes sliding at a position nearer to the impeller than to the bearing in an axial direction of the pump shaft; wherein a coaxial and annular groove is formed at the outer peripheral surface of the pump shaft and located at an axial position between the mechanical seal and the bearing thereby to prevent adhering water from transferring in a direction toward the bearing.

(q) The water pump as recited at (p), the annular groove has an axial width of not less than 2 mm.

The entire contents of Japanese Patent Applications P2010-263386, filed Nov. 26, 2010, are incorporated herein by reference.

Although the invention has been described above by reference to certain embodiments and examples of the invention, the invention is not limited to the embodiments and examples described above. Modifications and variations of the embodiments and examples described above will occur to those skilled in the art, in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. A water pump comprising: a pulley including a cylindrical section located radially inward of an outer periphery of the pulley, the pulley being rotatable upon transmission of power from a driving force; a pump shaft disposed radially inward of the cylindrical section of the pulley and fixed to the cylindrical section, the pump shaft having a first end section on which the pulley is mounted; a first flange wall extending from a first axial end portion of the cylindrical section of the pulley in a direction of the pump shaft; an impeller disposed at a second end section of the pump shaft; a pump housing including a tubular section disposed to surround the pump shaft; a mechanical seal disposed between a radially inward side of the tubular section of the pump housing and an outer peripheral surface of the pump shaft; and a bearing disposed between an inner peripheral surface of the cylindrical section of the pulley and the tubular section of the pump housing to rotatably support the pulley on the tubular section of the pump housing; wherein the pump shaft includes a coaxial small diameter shaft section located at its first part which is located axially between the mechanical seal and the flange wall, the small diameter shaft section having a diameter smaller than a diameter of a second part of the pump shaft on which the mechanical seal is disposed, the small diameter shaft section having an outer peripheral surface located radially inward of an outer peripheral surface of a third part of the pump shaft axially extending from the second part so as to form a first annular step portion.
 2. A water pump as claimed in claim 1, wherein the outer peripheral surface of the third part of the pump shaft and the outer peripheral surface of the small diameter shaft section are connected to each other through at least one annular face which is perpendicular to an axis of the pump shaft or tapered in a direction approaching the mechanical seal.
 3. A water pump as claimed in claim 1, wherein the tubular section of the pump housing includes a first portion defining thereinside a drain chamber for storing a liquid having a volume, and a second portion defining a drain hole for introducing liquid dropped from the annular step portion into the drain chamber, the drain chamber and the drain hole being located under the first annular step portion in a direction of gravity.
 4. A water pump as claimed in claim 1, wherein the outer peripheral surface of the small diameter shaft section of the pump shaft is cylindrical.
 5. A water pump as claimed in claim 1, wherein the small diameter shaft section of the pump shaft is formed at a part of the pump shaft, the diameter of the small diameter shaft section being smaller than a diameter of a fourth part of the pump shaft extending to the first end section of the pump shaft, the outer peripheral surface of the small diameter shaft section being located radially inward of an outer peripheral surface of the fourth part of the pump shaft so as to form a second annular step portion.
 6. A water pump as claimed in claim 5, wherein the outer peripheral surface of the fourth part of the pump shaft and the outer peripheral surface of the small diameter shaft section are connected to each other through at least one annular face which is perpendicular to an axis of the pump shaft or tapered in a direction away from the first flange wall.
 7. A water pump as claimed in claim 3, wherein the drain chamber is open to the atmosphere.
 8. A water pump as claimed in claim 7, wherein the tubular section of the pump housing includes a third portion defining thereinside an annular space chamber located around the outer peripheral surface of the small diameter shaft section, and a fourth portion defining a vent opening for venting vapor, the drain hole being formed above the annular space chamber in the direction of gravity, the vent opening being formed below the annular space chamber in the direction of gravity.
 9. A water pump as claimed in claim 1, wherein the pump shaft is formed continuously tapered in an axial direction of from side of the flange wall to side of the impeller, the outer peripheral surface of the third part of the pump shaft and the outer peripheral surface of the small diameter shaft section being connected through at least one annular face forming the first annular step portion, the annular face being perpendicular to the axis of the pump shaft.
 10. A water pump as claimed in claim 1, wherein the pulley includes a second flange wall extending from the cylindrical section at a second axial end portion opposite to the first axial end portion, and a belt installation section which axially extends from an outer peripheral portion of the second flange wall.
 11. A water pump as claimed in claim 1, wherein the pulley and the first flange wall are formed integral with each other.
 12. A water pump as claimed in claim 11, wherein the pump shaft and the first flange wall are formed separate from each other, the first end section of the pump shaft being fixed to the first flange wall.
 13. A water pump as claimed in claim 1, wherein the first flange wall is formed with a plurality of through-holes.
 14. A water pump as claimed in claim 1, wherein the first annular step portion is formed to have a plurality of annular step portions.
 15. A water pump as claimed in claim 14, wherein the small diameter shaft section includes a plurality of coaxial small diameter shaft sections so as to form a plurality of annular step portions.
 16. A water pump as claimed in claim 1, wherein the bearing includes an inner race, an outer race, and a bearing seal which is fixed to one of the inner and outer races and slidable to the other race.
 17. A water pump as claimed in claim 1, wherein the outer peripheral surface of the small diameter shaft section is located radially inward of the outer peripheral surface of the third part of the pump shaft by not less than 1 mm which corresponds to a height of the annular step portion.
 18. A water pump comprising: a pulley including a cylindrical section located radially inward of an outer periphery of the pulley, the pulley being rotatable upon transmission of power from a driving force; a pump shaft disposed radially inward of the cylindrical section of the pulley and fixed to the cylindrical section, the pump shaft having a first end section on which the pulley is mounted; a flange wall extending from an axial end portion of the cylindrical section of the pulley in a direction of the pump shaft; an impeller disposed at a second end section of the pump shaft; a pump housing including a tubular section disposed to surround the pump shaft; a mechanical seal disposed between a radially inward side of the tubular section of the pump housing and an outer peripheral surface of the pump shaft; and a bearing disposed between an inner peripheral surface of the cylindrical section of the pulley and the tubular section of the pump housing to rotatably support the pulley on the tubular section of the pump housing; wherein the pump shaft includes a step portion located axially between the mechanical seal and the flange wall to restrict movement of adhering water transferred through the outer peripheral surface of the pump shaft from side of the mechanical seal in a direction toward the flange wall.
 19. A water pump comprising: a pump shaft having a first end section on which a pulley is disposed and a second end section on which an impeller is disposed; a pump housing disposed surrounding an outer peripheral side of the pump shaft; a bearing disposed to the pump housing to rotatably supporting the pump shaft; and a mechanical seal fixed to the pump housing and to the pump shaft and having a seal section which makes sliding at a position nearer to the impeller than to the bearing in an axial direction of the pump shaft; wherein a coaxial and annular groove is formed at the outer peripheral surface of the pump shaft and located at an axial position between the mechanical seal and the bearing to prevent adhering water from transferring in a direction toward the bearing.
 20. A water pump as claimed in claim 19, wherein the annular groove has an axial width of not less than 2 mm. 